A method of processing an image of the fingerprint of an individual of the prior art is known, which comprises an acquisition part during which the image thus captured is either compared with reference images or converted into a template that is compared with reference templates.
The identification part of the processing method continues with an identification of the individual if the comparison is positive and non-identification of the individual if the comparison is negative.
The processing method of the prior art is implemented in a processing device comprising an exposure window behind which capture means are disposed.
The image of the imprint can be captured in two distinct ways.
The capture can be made with contact. The image of the imprint is then captured when the finger is in contact with the exposure window. Capture with contact makes it possible to capture images of imprints that are compatible with the majority of existing databases of imprints or templates after conversion.
Capture with contact of the image can be made through a prism and the image is then obtained by virtue of the optical coupling that takes place between the skin and the exposure window and in particular by virtue of the total reflection that is effected on the contact zones between the exposure window and the finger and which allows an increase in contrast. Optical coupling is greatly dependent on the environment, for example in the case of a dry finger the coupling does not take place correctly. One solution then consists of adding a special coating on the exposure window. Such a coating is fragile and the exposure window must then be regularly checked or even replaced.
Capture with contact can take place through a window. The phenomenon of total reflection is no longer used and the capture is no longer dependent on optical coupling. On the other hand, such a capture is greatly dependent on the squashing of the finger and therefore of the imprint on the window. There are few shadows generated and such a capture makes it possible to collect only a small quantity of information. There is then a reduction in contrast related to shadows during contact and therefore losses of information because of the squashing of the imprint.
Capture can take place without contact. The image of the imprint is then captured without the latter being in contact with the exposure window. Capture without contact makes it possible to capture images of the undeformed fingerprint and thus to collect more information characteristic of the imprint on such images than on images with contact, because of better contrast. However, the images of imprints collected are not interoperable with the majority of existing databases of imprints or templates.
The document entitled “The Surround Imager: A Multi-camera Touchless Device to Acquire 3D Rolled-Fingerprints” discloses an imprint capture device without contact, contactless acquisition avoiding deformations of the imprint on an exposure window. The images thus captured are then processed in order to construct a 3D representation of the said imprint.
Since existing imprint databases are based on images of imprints captured with contact, the image of the contactless imprint must be deformed so as to be compatible with the images in existing databases.
To this end, the 3D representation of the imprint is, in the document of the prior art, electronically deformed so as to reproduce the squashing of the imprint on the exposure window. The deformation is here generated automatically without its being necessary to have recourse to an image of the imprint captured with contact.
Such a method that does not take into account the specific elements of each imprint does not make it possible to obtain the best possible results.